Friday, October 31, 2014

IoT inspired: multi plug modified with SSR for AC control with a microcontroller

Yours truly is no stranger to controlling AC (Alternate Current, not Air Condition) with the use of microcontroller based system. In the previous posts, there were several iterations of arduino sous vide; controlling a SSR (Solid State Relay) or mech Relay to on/off AC connected to the heating element via a digital output from the microcontroller.

Fancy using an smart phone app to control the AC electrical appliances e.g lighting over the Internet? No matter what are your motivation to control AC with a microcontroller based system, then the setup below to control on AC appliance may satisfy.

The AC controlling circuit from the previous iterations are not elegant. The leads from AC are exposed, one way or the other. A wire exposed for termination posed a risk to the untrained. The following picture describes the exposed AC leads connecting to a microcontroller based system, even with the use of a terminal block.

The hazards are real: assuming a user touches the exposed end (circle in red in the picture above), or the wiring connection is loose, or worst,a stupid attempt at a cheap stunt.

Ever since the first inception of the microcontroller based AC control circuit, the search is on for the "perfect", fully enclosed, risk free implementation. On a casual saturday strolling along the street, yours truly chance upon a small tuck shop and a transparent multi plug with enough space to hold the SSR PCB https://www.sparkfun.com/products/10684 . The rest is history.

This implementation requires a multi plug, and a SSR PCB.

Warning: Potential hazard to human. Do not attempt this hack while multiplug is on a live connection. Do not attempt to touch the exposed ends when live. Ensure human is properly insulated from ground with rubber sole shoes.

1. Dismantle the multiplug, and make space for the SSR PCB

2. some electrical tape is used to insulate the exposed end from coming into contact with the SSR PCB

3. Drill a hole (circle in red) on the multi plug to accommodate 3 wires (VCC, GND, SIG) to the SSR PCB. Remove some of the brass contact (square in red) on the live wire connection. The remove ends will be soldered with wires to be connected to the SSR PCB. Use electrical tape as necessary to insulate the exposed ends.

4. Solder electrical wire to the exposed ends of the live connection, circled red in the picture below

6. Examine, label, test. In the following picture, circled in red is where the live connection is broken, and then the exposed ends soldered with electrical wires. These wires are then secured on the LOAD side of the SSR PCB. Test this modification of the multi plug only on a live system that is equipped with a functional ELCB http://en.wikipedia.org/wiki/Earth_leakage_circuit_breaker

user view of the modified multi plug with SSR

6. Observations
This is not the most elegant solution yet. The electrical wires (multicore) suffer from wire fatigue; due to the constant wiggling, twisting, and securing to the connector in a very compact space within the multi plug. Nonetheless, there are no AC exposed ends that might posed a risk to the end user. Plug the VCC, GND, SIG wires to a microcontroller, load some IoT inspired code and now you are ready to control AC electrical appliance over the Internet.

IoT SSR multiplug in action; using D7 on arduino to on and off SSR at 1second interval